1. Field of the Invention
This invention relates generally to methods and apparatus used to ensure that cleaned items are substantially free of biological and/or chemical contaminants and more particularly to methods that are especially useful to ensure the sterility of lumened medical items such as endoscopes.
2. Description of the Related Art
The cleaning and decontamination of items that come into contact with the bodily substances of people or animals such that they are substantially “substance free” (of, e.g., viruses, bacteria, detergent, sterilant, lipids, etc.) represent an immense and ongoing challenge. This challenge has been underscored by a recent article entitled “Widely used sterilizer under attack” (published in Jan. 21, 2003 edition of the newspaper USA Today). The article describes a fatal outbreak of bacterial infection that was linked to the improper sterilization of hospital bronchoscopes. Despite the hospital's use of one of the most popular sterilizing systems, tests performed by the Centers for Disease Control and Prevention found bacteria on the system's water filters and in its rinse water. This and other infection outbreaks has led to continuing controversy over how best to clean and sterilize used endoscopes.
The contaminants typically found on tubular or “lumened” medical items, such as endoscopes, are especially difficult to remove. In addition to fecal mater, loose cellular debris, blood and blood products, viruses, and bacteria, an endoscope can be coated with various hydrophobic films, such as “biofilm” material. A biofilm typically comprises cells, both dead and alive, cell debris and extracellular polymer substances. Once biofilm is formed by microorganisms (including bacteria, fungi, and protozoans), these microorganisms can colonize and replicate on the interior surfaces of tubing, forming a protective slime layer known as a “glycocalyx” that is especially difficult to remove.
Merely soaking endoscopes in a sterilant or detergent is unacceptable since numerous pockets exist within the tubing where the sterilant or detergent cannot reach effectively, which leaves areas of contamination within the endoscope. Moreover, with the prevalence of highly contagious diseases such as hepatitis B and C and Acquired Immune Deficiency Syndrome, reliable sterilization or disposal of all used medical tools seemingly becomes mandatory. Yet, while many medical instruments today are routinely cleaned, disinfected, and reused, experts in the field recently have warned that some of the more difficult to clean and sterilize medical items are putting people at risk.
Indeed, one expert has stated that there are no independent published reports or data anywhere in the medical literature that show liquid chemical sterilants (or any other method/process/agent) can be used to reliably “sterilize” flexible endoscopes or other complex, lumened instruments (See Comments by L. Muscarella (Custom Ultrasonics) on AAMI TIR7:1999, Chemical Sterilants and Sterilization Methods: A Guide to Selection and Use, downloaded from the website myendosite.com).
To the contrary, Kovacs et al. reports that a strain of Pseudomonas aeruginosa has been repeatedly isolated from tap water used for cleaning and rinsing endoscopes and appears to be responsible for three separate clinical episodes of endoscopic retrograde cholangio-pancreatography (ERCP)-associated cholangitis over an 11-yr period. These authors also conclude that the organism is resistant to a commonly used sterilant because it was recovered from a variety of endoscopes that had undergone stringent reprocessing protocols (see Kovacs B J, et al. “Efficacy of various disinfectants in killing a resistant strain of Pseudomonas aeruginosa by comparing zones of inhibition: Implications for endoscopic equipment reprocessing,” Am J Gastroenterol 1998;93:2057-9). Thus, there is a genuine need for “overkill” sterilization to help ensure that even chemical-resistant pathogens are effectively eliminated.
In addition to the infection issues, environmental concerns over the content of medical item wash or rinse water effluent have become more pronounced as the detrimental effects (including toxicity) of various cleaning and sterilizing chemicals are now better understood. For example, commonly used liquid chemical sterilants, such as glutaraldehyde and paracetic acid, are known to have adverse health effects or carcinogenic activity. Since most endoscope cleaning and sterilization is accomplished with various detergents in combination with glutaraldehyde or paracetic acid, harmful chemical residue can be left behind both on the item and in the wash or rinse effluent. Therefore, discharge of these chemicals into rivers, lakes, and even sewer systems raises safety issues that have yet to be addressed.
Furthermore, some chemical cleaners or sterilants are so harshly reactive that they can damage the items they are meant to clean or sterilize. Thus, the problems encountered during item (and especially medical item) cleaning and disinfecting primarily involve trying to strike a balance between ensuring as much as possible the complete removal of contaminants and chemicals while, at the same time, not damaging the instrument or the environment.
Even the simple act of rinsing medical items with filtered water after cleaning or sterilization has been called into question. After sterilization, endoscopes typically are rinsed with water filtered down to the 0.2 micron (200 nanometer) level. Unfortunately, many viruses, endotoxins, and prions are smaller than 200 nanometers, meaning that they can remain in the water even after filtration. Also, as reported in the articles mentioned above, water and water filters are known sources of contamination. Even more troubling, however, is the statement by one expert that “there are no independent data in the medical literature that support the production of sterile water (defined as containing fewer than 10−6 CFU/ml and fewer than 5 endotoxin units/ml) by passing unprocessed water (that is, unsterilized water, such as water that flows though a hospital's tap) through a bacterial (e.g., 0.1 or 0.2 micron) filtration system” (See Comments by L. Muscarella (Custom Ultrasonics) on AAMI TIR7:1999, Chemical Sterilants and Sterilization Methods: A Guide to Selection and Use, downloaded from the website myendosite.com). Moreover, there is no currently available system that monitors the biological content of filtered water to insure its sterility when used in conjunction with medical item cleaning or sterilization apparatuses. Finally, having to add additional sterilization steps and/or use sterilized (e.g., autoclaved) water becomes tedious and expensive.
Ozone is a well known sterilant. Ozone was first used for drinking water treatment in 1893 in the Netherlands. While being used frequently in Europe for drinking water disinfection, it was slow to transfer to the United States. Indeed, early application of ozone for water treatment in the United States was primarily for non-disinfection purposes such as color removal or taste and odor control. Today, ozone also is known to oxidize oils and reduce scale build-up. Nonetheless, the strongly oxidative qualities of ozone also present problems in that the use of ozone for the cleaning and disinfecting of items will often result in permanent damage to the item, especially if it is exposed to ozone for long periods while attempting to completely clean and decontaminate all surfaces.
Thus, while ozone applications to water and water line disinfection are now fairly common, these methods have not become widespread in other sterilization applications because they rely on a treatment system that reticulates ozonated water through the entire treatment area during repeated cleaning cycles in order to achieve and maintain disinfection. Such constant treatment is not possible for most items (and especially medical items) due to the damage that continual or repeated exposure to ozone would cause.
Even with recent advances in cleaning devices and methods, such as those invented by Langford (see, for example, U.S. Pat. No. 5,443,801), there still remains the problem of balancing the need for complete cleaning, disinfection, and degradation of all chemical residues on an item with preventing or mitigating damage to that item and to the environment.
Therefore, there continues to be a need for a cleaning and decontaminating method that, without damaging the item being treated, helps to ensure sterility, assists in loosening difficult soiling, such as biofilm-entrained contaminants and other hydrophobic compositions or films, and degrades chemicals so that effluent is substantially free of harmful residues.